30 min

Split the I2C bus into several sub-branches with PCA9518 and STM32F042K6 to resolve address conflict issues

I2C multiplexing

I2C MUX 6 Click with UNI Clicker

Published May 31, 2023

Click board™

I2C MUX 6 Click

Development board

UNI Clicker


NECTO Studio



Expandable buffer designed for I2C and SMBus applications offering four bidirectional data transfer channels



Hardware Overview

How does it work?

I2C MUX 6 Click is based on the PCA9518, an expandable four-channel bidirectional buffer controllable through the I2C serial interface from Texas Instruments. The primary SCL/SDA signal pair is directed to four channels where only one SCL/SDA channel can be selected at a time, determined by the state of the four Enable pins, routed to the AN, RST, CS, and PWM pins of the mikroBUS™ socket. The PCA9518 overcomes the restriction of maximum bus capacitance by separating and buffering the I2C data (SDA) and clock (SCL) lines into multiple groups of 400pF I2C channels. The PCA9518 has several multi-directional open-drain buffers designed to support the standard low-level-contention arbitration of the I2C bus. Except during arbitration, the PCA9518 acts like

a pair of non-inverting open-drain buffers, one for SDA and one for SCL. It can communicate with other PCA9518 hubs through a 4-wire inter-hub expansion bus located on the onboard header with EXP labeled pins, i.e., permits extension of the I2C-bus by buffering the data (SDA) and the clock (SCL) lines enabling virtually an unlimited number of buses of 400pF. The PCA9518 communicates with MCU using the standard I2C interface that supports Standard-Mode (100 kHz) and Fast-Mode (400 kHz) operations. As mentioned, each Enable pin, ENx, controls its associated SDAx and SCLx channels. When the ENx pin is in a low logic state, it isolates its corresponding SDAx and SCLx lines from the system by blocking the inputs from SDAx and SCLx and disabling the output drivers on these lines.

It is essential that the ENx change state only when both the global bus and the local port are in an IDLE state to prevent system failures. This Click board™ is designed for 3.3V operation. It also has onboard terminals labeled as VCC-I2C to supply a logic voltage of 3.3V or 5V for PCA9518’s I2C lines, which are 5V-tolerant. However, the board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. The Click board™ comes equipped with a library containing functions and an example code that can be used, as a reference, for further development.


Features overview

Development board

UNI Clicker is a compact development board designed as a complete solution that brings the flexibility of add-on Click boards™ to your favorite microcontroller, making it a perfect starter kit for implementing your ideas. It supports a wide range of microcontrollers, such as different ARM, PIC32, dsPIC, PIC, and AVR from various vendors like Microchip, ST, NXP, and TI (regardless of their number of pins), four mikroBUS™ sockets for Click board™ connectivity, a USB connector, LED indicators, buttons, a debugger/programmer connector, and two 26-pin headers for interfacing with external electronics. Thanks to innovative manufacturing technology, it allows you to build

gadgets with unique functionalities and features quickly. Each part of the UNI Clicker development kit contains the components necessary for the most efficient operation of the same board. In addition to the possibility of choosing the UNI Clicker programming method, using a third-party programmer or CODEGRIP/mikroProg connected to onboard JTAG/SWD header, the UNI Clicker board also includes a clean and regulated power supply module for the development kit. It provides two ways of board-powering; through the USB Type-C (USB-C) connector, where onboard voltage regulators provide the appropriate voltage levels to each component on the board, or using a Li-Po/Li

Ion battery via an onboard battery connector. All communication methods that mikroBUS™ itself supports are on this board (plus USB HOST/DEVICE), including the well-established mikroBUS™ socket, a standardized socket for the MCU card (SiBRAIN standard), and several user-configurable buttons and LED indicators. UNI Clicker is an integral part of the Mikroe ecosystem, allowing you to create a new application in minutes. Natively supported by Mikroe software tools, it covers many aspects of prototyping thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

UNI clicker double image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M0

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Channel 1 Enable
Channel 2 Enable
Channel 3 Enable
Power Supply
Channel 4 Enable
I2C Clock
I2C Data

Take a closer look


I2C MUX 6 Click Schematic schematic

Step by step

Project assembly

UNI Clicker front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI Clicker as your development board.

UNI Clicker front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for STM32F745VG front image hardware assembly
Prog-cut hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
UNI Clicker Access MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
Necto image step 5 hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto No Display image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Debug Image Necto Step hardware assembly

Track your results in real time

Application Output

After loading the code example, pressing the "DEBUG" button builds and programs it on the selected setup.

Application Output Step 1

After programming is completed, a header with buttons for various actions available in the IDE appears. By clicking the green "PLAY "button, we start reading the results achieved with Click board™.

Application Output Step 3

Upon completion of programming, the Application Output tab is automatically opened, where the achieved result can be read. In case of an inability to perform the Debug function, check if a proper connection between the MCU used by the setup and the CODEGRIP programmer has been established. A detailed explanation of the CODEGRIP-board connection can be found in the CODEGRIP User Manual. Please find it in the RESOURCES section.

Application Output Step 4

Software Support

Library Description

This library contains API for I2C MUX 6 Click driver.

Key functions:

  • i2cmux6_set_channel This function sets the desired channel active and configures its slave address.

  • i2cmux6_generic_write This function writes a desired number of data bytes starting from the selected register by using the I2C serial interface.

  • i2cmux6_generic_read This function reads a desired number of data bytes starting from the selected register using the I2C serial interface.

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief I2CMUX6 Click example
 * # Description
 * This example demonstrates the use of I2C MUX 6 click board by reading the
 * device ID of a 6DOF IMU 11 and Compass 3 click boards connected to 
 * the channels 1 and 4 respectfully.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initializes the driver and logger.
 * ## Application Task
 * Reads the device ID of the connected click boards.
 * Channel 1 : 6DOF IMU 11 click [slave address: 0x0E; reg: 0x00; id: 0x2D],
 * Channel 4 : Compass 3 click   [slave address: 0x30; reg: 0x2F; id: 0x0C].
 * All data is being logged on the USB UART where you can check the device ID.
 * @note
 * Make sure to provide 3v3 power supply on VCC-I2C pin.
 * @author Stefan Filipovic

#include "board.h"
#include "log.h"
#include "i2cmux6.h"

#define DEVICE0_NAME                "6DOF IMU 11 click"
#define DEVICE0_POSITION            I2CMUX6_CHANNEL_1
#define DEVICE0_SLAVE_ADDRESS       0x0E
#define DEVICE0_REG_ID              0x00
#define DEVICE0_ID                  0x2D

#define DEVICE1_NAME                "Compass 3 click"
#define DEVICE1_POSITION            I2CMUX6_CHANNEL_4
#define DEVICE1_SLAVE_ADDRESS       0x30
#define DEVICE1_REG_ID              0x2F
#define DEVICE1_ID                  0x0C

static i2cmux6_t i2cmux6;
static log_t logger;

void application_init ( void ) 
    log_cfg_t log_cfg;  /**< Logger config object. */
    i2cmux6_cfg_t i2cmux6_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.
    i2cmux6_cfg_setup( &i2cmux6_cfg );
    I2CMUX6_MAP_MIKROBUS( i2cmux6_cfg, MIKROBUS_1 );
    if ( I2C_MASTER_ERROR == i2cmux6_init( &i2cmux6, &i2cmux6_cfg ) ) 
        log_error( &logger, " Communication init." );
        for ( ; ; );
    log_info( &logger, " Application Task " );

void application_task ( void ) 
    uint8_t device_id;
    if ( I2CMUX6_OK == i2cmux6_set_channel ( &i2cmux6, DEVICE0_POSITION, DEVICE0_SLAVE_ADDRESS ) )
        log_printf( &logger, "\r\n Active Channel: - " );
        for ( uint8_t cnt = 0; cnt < 4; cnt++ )
            if ( ( DEVICE0_POSITION ) & ( 1 << cnt ) )
                log_printf( &logger, "%u - ", ( uint16_t ) ( cnt + 1 ) );
        if ( I2CMUX6_OK == i2cmux6_generic_read ( &i2cmux6, DEVICE0_REG_ID, &device_id, 1 ) )
            log_printf( &logger, "\r\n %s - Device ID: 0x%.2X\r\n", ( char * ) DEVICE0_NAME, ( uint16_t ) device_id );
        Delay_ms( 1000 );
    if ( I2CMUX6_OK == i2cmux6_set_channel ( &i2cmux6, DEVICE1_POSITION, DEVICE1_SLAVE_ADDRESS ) )
        log_printf( &logger, "\r\n Active Channel: - " );
        for ( uint8_t cnt = 0; cnt < 4; cnt++ )
            if ( ( DEVICE1_POSITION ) & ( 1 << cnt ) )
                log_printf( &logger, "%u - ", ( uint16_t ) ( cnt + 1 ) );
        if ( I2CMUX6_OK == i2cmux6_generic_read ( &i2cmux6, DEVICE1_REG_ID, &device_id, 1 ) )
            log_printf( &logger, "\r\n %s - Device ID: 0x%.2X\r\n", ( char * ) DEVICE1_NAME, ( uint16_t ) device_id );
        Delay_ms( 1000 );

void main ( void ) 
    application_init( );

    for ( ; ; ) 
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support